Sensible Heat Ratio - SHR

The Sensible Heat Ratio - SHR - is used to describe the ratio of sensible heat load to total heat load and can be expressed as:

SHR = q_s / q_t

= q_s / (q_s + q_l)                                                (1)

where

SHR = sensible heat ratio (ratio of sensible heat load to total heat load)

q_s = sensible heat load (kW, Btu/hr)

q_t = total heat load - sensible heat and latent heat (kW, Btu/hr)

q_l = latent heat load (kW, Btu/hr)

For an air flow (1) can be modified to:

SHR = c_p (t_o - t_i ) / (h_o - h_i)                                              (2)

where

c_p = specific heat air (1.005 kJ/kg ^oC, 0.240 Btu/lb ^oF)

t_o = outlet air temperature (^oC, ^oF)

t_i = inlet air temperature (^oC, ^oF)

h_o = outlet moist air enthalpy (kJ/kg, Btu/lb)

h_i = inlet moist air enthalpy (kJ/kg, Btu/lb)

Example - SHR for a room

The inlet temperature to a room with some people is 20 ^oC. The relative moisture of the inlet air is 50%. From the Mollier chart the enthalpy of the inlet air is 37 kJ/kg.

The outlet temperature is 26 ^oC and the relative moisture of the outlet air is 40%. From the Mollier chart the enthalpy of the outlet air is 47 kJ/kg.

The Sensible Heat Ratio can be calculated as

SHR = (1.005 kJ/kg ^oC) ((26 ^oC) - (20 ^oC)) / ((47 kJ/kg) - (3 7 kJ/kg))

= 0.6

60% of the load provided to the room heats the air (sensible load) and 40% of the load provided humidifies the air (latent load).

Example - SHR for a evaporator

If the SHR value for an evaporator is 75% (0.75) - 75% of the load cools the air (sensible load) and 25% of the loads dehumidifies the air (latent load).

General Design Values

• Auditoriums, Theaters - SHR : 0.65 - 0.75
• Apartments - SHR : 0.80 - 0.95
• Banks, Court Houses, Municipal Buildings - SHR : 0.75 - 0.90
• Churches - SHR : 0.65 - 0.75
• Dining Halls - SHR : 0.65 - 0.80
• Computer Rooms - SHR : 0.80 - 0.95
• Cocktail Lounges, Bars, Taverns, Clubhouses, Nightclubs - SHR : 0.65 - 0.80
• Jails - SHR : 0.80 - 0.95
• Hospital Patient Rooms, Nursing Home, Patient Rooms - SHR : 0.75 - 0.85
• Kitchens - SHR : 0.60 - 0.70
• Libraries, Museums - SHR : 0.80 - 0.90
• Malls, Shopping Centers - SHR : 0.65 - 0.85
• Medical/Dental Centers, Clinics and Offices - SHR : 0.75 - 0.85
• Motel and Hotel Public Areas - SHR : 0.75 - 0.90
• Motel and Hotel Guest Rooms - SHR : 0.80 - 0.95
• Police Stations, Fire Stations, Post Offices - SHR : 0.75 - 0.90
• Precision Manufacturing - SHR : 0.80 - 0.95
• Restaurants - SHR : 0.65 - 0.80
• Residences - SHR : 0.80 - 0.95
• Retail, Department Stores - SHR : 0.65 - 0.90
• Other Shops - SHR : 0.65 - 0.90
• School Classrooms - SHR : 0.65 - 0.80
• Supermarkets - SHR : 0.65 - 0.85